1. Field of the Invention
The present invention relates to a Switched Reluctance Motor (SRM), and more particularly to a self-excited reluctance motor capable of generating a rotating force with a simple commutator made based on a classical commutation theory, without using a commutation logic of an electric circuit, or making any changes to characteristics of a conventional SRM.
2. Description of the Related Art
Generally, a Switched Reluctance Motor (SRM) rotates at a relatively higher speed with a simpler structure, when compared to an induction motor. Also, by using a semiconductor element as a switch for controlling electric power, the SRM not only has an accurate control on various functions are possible, but also has a higher efficiency. For such advantages of the SRM, there have been many researches and developments of SRM.
As shown in FIG. 1, the SRM simply includes a stator 1 and a rotator 3 without a commutator. The SRM has a dual-pole structure which has stator poles 2 and rotator poles 4. The rotator 3 is formed of silicon steel plates which are stacked on each other firmly. In the stator 1, two opposing stator poles 2 are connected by a wire in parallel or series in order to generate a magnetic flux toward the same direction.
The SRM mainly includes a 6/4 pole SRM having six stator poles and four rotator poles, a 12/8 pole SRM having twelve stator poles and eight rotator poles, and 24/16 pole SRM having twenty-four stator poles and sixteen rotator poles.
Among these, a driving principle and method of the SRM will be described, with reference to an example of 3-phase 12/8 pole SRM.
First, the driving principle of the SRM will be described with reference to FIGS. 1 and 2. FIG. 1 is a sectional view of a conventional 3-phase 12/8 pole SRM. Although FIG. 1 shows only certain stator poles 2 being wound by coils for a more convenient explanation thereof, it will be fully understood by those skilled in art that the other stator poles 2 are also wound by phase-A, phase-B, and phase-C coils in the same manner.
When electric voltage is applied to a wire (a-axe2x80x2) winding the stator poles 2a and 2axe2x80x2, the stator poles 2a and 2axe2x80x2 are excited, and the neighboring rotator poles 4 are rotated in the direction of arrow of FIG. 1, to be aligned with the stator poles 2a and 2axe2x80x2 which are excited. Before the alignment of the excited stator poles 2a and 2axe2x80x2 and the neighboring rotator poles 4, the electric voltage supply to the wire (a-axe2x80x2) is cut off. Next, electric voltage is supplied to the neighboring stator wire (b-bxe2x80x2), and the stator poles 2b and 2bxe2x80x2 are excited. Accordingly, in the same manner as described above, the neighboring rotator poles 4 of the newly excited stator poles 2b and 2bxe2x80x2 are rotated in the direction of arrow of FIG. 1 to be aligned with the newly excited stator poles 2b and 2bxe2x80x2. As the stator poles 2a and 2axe2x80x2, 2b and 2bxe2x80x2, and 2c and 2cxe2x80x2 are sequentially excited in the above-described manner, the rotator 3 is continuously rotated.
FIGS. 2(a) to 2(b) are sectional views for showing the positions of the rotator poles 4 with respect to excited stator poles 2 of the 12/8 pole SRM. As shown in FIG. 2(a), when the rotator poles 4b are aligned with the excited stator poles 2a and 2axe2x80x2 in a straight line (hereinafter called alignment position), a torque is not generated even when electric current flows in the stator wire (a-axe2x80x2). Meanwhile, as shown in FIGS. 2(c) and 2(d), when the rotator poles 4b are out of alignment position with the stator poles 2a and 2axe2x80x2, the rotator 3 generates a torque to go to the alignment position.
As shown in FIG. 2(b), when middle points of the neighboring poles 4a and 4b, and 4c and 4d of the rotator 3 are aligned with the excited stator poles 2a and 2axe2x80x2 in straight lines (Q: non-alignment position), as in the alignment state, a torque is not generated even when electric current flows in the stator wire (a-axe2x80x2). If the rotator poles 4 are out of the alignment position even by a slight degree, the excited stator poles 2 attract the nearest rotator poles 4 to a new alignment position, generating a torque.
As shown in FIGS. 2(c) and 2(d), when the rotator poles 4 are not in the alignment or non-alignment position, and when electric current flows in the stator wire (a-axe2x80x2, b-bxe2x80x2, or c-cxe2x80x2) of the stator poles 2a and 2axe2x80x2, 2b and 2bxe2x80x2, or 2c and 2cxe2x80x2, a torque is generated to align the rotator 3 to the alignment position as in FIG. 2(a).
Next, a driving circuit for driving the 3-phase 12/8 pole SRM will be described. In order to drive the SRM, a driving converter is required. Generally, the driving converter has to i) supply a voltage to a wire of a stator pole 2 which corresponds to a rotator pole 4, ii) control or maintain the electric current at a suitable level for exciting the stator pole 2, and iii) supply a backward voltage for electric current extinction at an excited phase. The requirement iii) is mainly conducted by a diode.
Currently, many converter topologies have been studied to control the SRM, in a manner of reducing converter manufacturing cost by reducing a number of switching elements, and also improving a controlling performance.
As a driving converter, there mainly are Asymmetric Bridge Converter, BifillarWinding Converter, Split-Source Converter, Capacitor-Dump converter, Resistor-Dump Converter, and Switch-Shared Converter available at the present time. Among these converters, the driving method of the driving converter will now be described briefly with a reference to an example of the Asymmetric Bridge Converter.
FIG. 3 is a circuit diagram for showing a conventional Asymmetric Bridge Converter, especially for showing an electric circuit for driving the 3-phase 12/8 pole SRM. As shown in FIG. 3, the Asymmetric Bridge Converter includes plural pairs of switches (transistor elements T1 and T2, T3 and T4, and T5 and T6) and diodes (D1 and D2, D3 and D4, and D5 and D6).
In the electric circuit, by turning on and thus supplying Direction Current voltage to the pair of switches T1 and T2, or T3 and T4, or T5 and T6 connected to phase-A, phase-B, or phase-C, the corresponding stator poles 2 are excited. While electric current flows in the stator wire, the level of electric current is controlled by selectively turning on or off one or both of the pair of switches T1 or/and T2, or T3 or/and T4, or T5 or/and T6. Accordingly, electric current circulates through one diode D1 or D2 and one switch T1 or T2, or circulates through both of the diodes D1 and D2, charging a condenser. Next, when the pair of switches T1 and T2 are turned off, electric current is dissipated. Here, before an inductance of corresponding phase draws a negative slope, the electric current should be reduced to an dissipation or to a negligible degree.
Since the conventional converter is formed of a plurality of electric elements, the structure thereof is complex, and the manufacturing cost increases. Accordingly, it is almost impossible to employ the converter in a low-price devices. Further, in order to control the switches T1 and T2, T3 and T4, and T5 and T6, a separate controlling means such as a microcomputer is required. Since a control algorithm also should be developed, it is hard to employ the converter to control the SRM.
The present invention has been made to overcome the above-mentioned problems of the related art, and accordingly, it is an object of the present invention to provide a selfexcited reluctance motor capable of generating a rotating force with a simple commutator and without having to use a high-price electric circuit.
The above object is accomplished by a self-excited reluctance motor according to the present invention, including a stator having a plurality of stator poles respectively wound by wires of different phases; a rotator having a plurality of rotator poles formed on an outer circumference thereof, the rotator rotatably inserted in the stator; and a commutator. The commutator includes a body coaxially arranged with the rotator, and formed of an insulating material; an electrode formed on an outer circumference of the commutator body; a plurality of switching portions formed on the outer circumference of the commutator body at a predetermined distance from each other, and connected with the electrode; a plurality of switching brushes electrically connected to stator wires of different phases and to the plurality of switching portions, for permitting an electric current to flow the respective stator wires; and an electrode brush electrically connected to an external power source and to the electrode.
Accordingly to the present invention, the switching portions are spaced from each other at an angle that the stator is rotated from a point where a certain stator pole and rotator pole are aligned with each other to a point where the next stator pole and rotator pole are aligned with each other. The switching portions are symmetrically formed in pairs on an outer circumference of the commutator body.
Further, the electrode includes a positive electrode and a negative electrode. The positive electrode is electrically connected to one of the switching portions and through an interior of the commutator body, while the negative electrode is electrically connected to the other one of the switching portion and through the interior of the commutator.
According to another aspect of the present invention, a number of the switching portions formed on the outer circumference of the commutator body corresponds to a number of places where the stator poles and the rotator poles are aligned with each other.
The switching brushes are spaced from each other at an angle that the stator is rotated from a point where a certain stator pole and rotator pole are aligned with each other to a point where the next stator pole and rotator pole are aligned with each other. The switching portions are formed on the outer circumference of the commutator body, and are spaced from each other at an angle of 90xc2x0.
According to the present invention, during the rotation of the commutator body and the rotator, the switching portions and switching brushes repeat electricity supply and cut-off with respect to the stator wires of the respective phases. Accordingly, a torque is generated at the rotator, and the rotator is continuously rotated.
Accordingly, without any switching operation of the circuit elements with respect to the respective phases, the rotator is continuously rotated by a mechanism of the commutator connected to the rotator, and thus, the motor is also continuously rotated.